Fibrous mat-faced gypsum board

ABSTRACT

An exterior finishing system for a building. including particularly an exterior insulation system, which includes a fibrous mat-faced gypsum board, preferably a board in which the set gypsum core thereof is water resistant, and preferably one in which the set gypsum core is sandwiched between two sheets of porous glass mat, with the outer surface of at least one of said mats being substantially free of set gypsum, and means for preparing the board, including control of the viscosity of the aqueous gypsum slurry from which the set gypsum core of the board is formed. Also, the use of fibrous mat-faced gypsum board as the shaft liner panel in a shaft wall assembly.

This is a divisional of co-pending application Ser. No. 583,874 filed onFeb. 27, 1984, now U.S. Pat. No. 4,647,496.

FIELD OF THE INVENTION

This invention relates to improvements in exterior finishing systemssuch as, for example, exterior insulation systems for buildings, andalso to improvements in shaft wall assemblies for buildings. Moreparticularly, this invention relates to an improved structural componentfor use as a support surface in an exterior finishing system, includingan exterior insulation system (sometimes referred to herein forconvenience as "EISystem"). In addition, the present inventionencompasses improvements in hollow shaft wall assemblies, for example,those used in constructing elevator shafts and stairwells.

This invention will be described initially in connection with its use inEISystems, but, as will be explained hereinafter, its use has widerapplicability.

EISystems are presently being used more and more widely to insulateexisting buildings and buildings under construction includingindustrial, commercial, municipal, institutional, and residentialbuildings. Installation of a typical EISystem in new constructiongenerally involves the following sequential steps: (A) constructing aframe for support of the outside wall of a building; (B) affixing to theframe structural panels to provide a smooth continuous surface for thesupport of other of the components of the EISystem; (C) affixing to thesupport surface panels of insulation; and (D) affixing to the panels ofinsulation a mesh-like material which in turn is covered with anexterior finishing material having weathering and aesthetic properties.Such systems are designed to be not only highly insulative in characterand attractive in appearance, but also weather resistant. EISystems canbe used to advantage to conserve energy used for heating and to conserveenergy used for air-conditioning.

EISystems have inherent advantages over interior insulating systems and,in addition, they can be used to better advantage than interiorinsulating systems in many applications.

For example, the range of temperature variation in structural componentscomprising the walls of a building insulated from the outside is lessthan that for such components in a building which is insulated from theinside. Accordingly, such structural components when insulated from theoutside are subjected to significantly lower amounts of stress caused bythermal expansion and contraction than those insulated from the inside.This is particularly advantageous in applications where the structuralcomponents comprise materials having markedly different coefficients ofexpansion, as is often the case. In addition, the interior space in abuilding having an EISystem tends to have a more uniform temperature andbe less drafty than that of a building insulated from the inside.

Certain buildings are not capable of being insulated from the interiorexcept that valuable inside space is lost to the system. Theinstallation of an EISystem does not disturb the inside space of thebuilding.

An EISystem can be used also to modernize or otherwise renovate theexterior of a building in need of renovation. Various of the EISystemswhich are commercially available give the architect a wide range ofaesthetically pleasing designs from which to choose. In addition, thecost of installing an EISystem is relatively low when there is takeninto account both the costs of other systems and the improved thermalefficiencies that can be realized. The relatively light weight of boththe insulation and the exterior finish in an EISystem is particularlyadvantageous in new construction because of reduced foundationrequirements.

There are, however, problems associated with the design and/orinstallation of EISystems. As will be discussed in detail below, variousof the problems stem from the type of material which is used as thesupporting member for the insulating and exterior finishing materials ofthe system. The present invention involves improvements in suchsupporting member.

Reported Developments

As mentioned above, a typical EISystem includes a supporting member towhich there is affixed insulating material, which in turn is coveredwith an exterior finishing material. An exemplary EISystem includes awood or metal frame which is mechanically held in place by nails orscrews to appropriate structural members of the building, with panels ofthe supporting member in turn mechanically affixed by nails or screws tothe frame. The supporting member, which typically consists of a smoothcontinuous surface comprising individual panels of material positionedin abutting relationship, must be strong enough to carry the weight ofthe components which overlie it, including the insulating and exteriorfinishing materials. Although low density, light weight insulatingpanels of expanded polystyrene are used widely in such systems, theexterior finishing material is generally a much denser and heavierweight material, for example, an acrylic resin/cement coating that mayinclude decorative aggregate embedded therein.

Certain of the commercialized EISystems include the use of panels of aPortland cement-based composition as the structural member for thesupport of the overlying panels of insulation and exterior finishingmaterial. It is believed that such cement-based panels are described inU.S. Pat. No. 3,284,980 which discloses a building panel comprising acore consisting of a mixture of hydraulic cement and light-weightaggregate (for example, perlite) sandwiched between sheets of fibrousmaterial (for example, woven glass fiber screen), which are adhered tothe faces of the core by separate layers of bonding material containingat least 50% hydraulic cement. Although the cores of such panels includea light-weight aggregate, the panels are nevertheless relatively heavy.For example, a panel 3'×4' and 7/16" in thickness weighs about 401/2pounds. The handling and installation of such panels lead to theconsumption of relatively large amounts of energy. This is a burden toworkmen and makes transportation of the panels relatively costly.

A material which is used more widely in EISystems than theaforementioned cement board is gypsum board, that is, panels comprisinga core of set gypsum (calcium sulfate dihydrate) sandwiched betweenpaper cover sheets. The particular type of gypsum board that isrecommended for use in EISystems is known as "gypsum sheathing" which isgypsum board designed for use on the exterior of buildings where itserves as an underlying surface which is covered with such materials asaluminum, wood siding, Portland cement stucco and, in the case of anEISystem, with insulating and exterior finishing materials. Conventionalgypsum sheathing, as opposed to conventional gypsum wallboard for use inthe interior of a building, includes a set gypsum core which containsone or more additives which improve the water resistance of the setcore. The gypsum core of commercially available wallboard can absorb asmuch as 40-50wt. % water when immersed therein at a temperature of 70°F. for about 2 hours. As the absorption of water tends to substantiallyreduce the strength of the core, materials which reduce the tendency ofthe core to absorb water are included therein. In addition, sheathinghas water-repellant paper cover sheets which shed water. This istemporary protection for the sheathing before it is installed and beforeit is covered with the exterior finishing material.

Gypsum sheathing has many desirable characteristics which make itsuitable for use in an EISystem. For example, such sheathing hasrelatively good fire-resistant properties, it is relatively light inweight, it has satisfactory water-resistant properties and it can bemechanically affixed in convenient fashion to a metal or wooden framewhich underlies the sheathing.

Notwithstanding the aforementioned, concerns have been expressedrespecting the use of such gypsum sheathing in EISystems. By way ofbackground, it is noted that it is conventional in the industry to affixpanels of insulating material to the underlying support of gypsumsheathing by the use of an adhesive material and, in turn, to affix bythe use of adhesive materials each of the plies which overlie the panelsof insulation. Except for the use of mechanical fastening means in theconstruction of the frame of the building and in affixing the gypsumsheathing to the frame, all of the components of the EISystem are ineffect glued together.

Tests designed to evaluate the cohesive strength of and the adhesivestrengths between the various components comprising the EISystem haveshown that initial failure (pulling apart) of the system occurs not inany of the adhesive layers, but in the paper cover sheet of the gypsumsheathing. Such cover sheet consists of multi-ply paper, for example, asmany as 7 layers of paper adhered together in a form that appears to theeye to be a monolithic sheet of paper. Accordingly, the cohesivestrength of the paper can be characterized as the weak portion of thesystem.

Another concern respecting the use of gypsum sheathing in EISystems ofthe aforementioned type is that water leakage through the system canlead to the deterioration of the bond between the paper cover sheet andthe gypsum core. (Although the system is designed to be waterproof,there are circumstances where defects in one or more plies of the systemand/or unusually severe environmental conditions are the cause of watersee page.) It should be appreciated that deterioration of this bond canlead to cracking of the exterior finish, and possibly even collapse ofportions of the system as the component which is adhered to the papercover sheet pulls apart.

In an effort to overcome the aforementioned type problems, it has beenproposed to affix the insulating material to the underlying gypsumsheathing by the use of mechanical fasteners which extend through theinsulating material, the core of the gypsum sheathing, and into theframe. This approach to the problem has the disadvantage that the worktime involved in installing the system is increased significantlyinasmuch as it is much more time consuming to install fasteners than toapply an adhesive. Another shortcoming of the fastener approach is thatthe fasteners provide paths for the flow of water which may penetratethe system and weaken the bond between the paper cover sheet and gypsumcore, as mentioned above.

Irrespective of how the insulating material is affixed to the underlyinggypsum sheathing, there is another problem connected with the use ofsheathing in EISystems. Because of its susceptibility to degradation bywater, care must be taken to protect the sheathing from rain and othermoisture conditions which may be encountered as the sheathing is storedat the job site awaiting use and during installation. Taking suchprotective precautions consumes time, causes inconvenience, andsometimes causes delays in installation of the system--all of which tendto increase costs.

Although gypsum sheathing has a water-repellant paper surface whichprovides some limited protection against water degradation, this type ofsurface forms a relatively poor bond with water-based adhesives whichare used to adhere to the surface other components of the EISystem.

The present invention is directed to use in EISystems of a supportmember comprising an improved gypsum-based structural component which ismodified in a manner such that problems of the type associated with theuse of conventional gypsum sheathing are either overcome or alleviatedsignificantly.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided an improvedstructural support element comprising a fibrous mat-faced gypsum supportsurface for use in an exterior finishing system, including exteriorinsulating systems, for buildings. One embodiment of the presentinvention comprises an exterior insulation system for a building whichincludes a fibrous mat-faced gypsum support surface facing away fromsaid building, insulating material having an inner surface and an outersurface, the inner surface of which is adhered to said support surfaceby an adhesive material, the insulating material being substantiallyfree of channels penetrating therethrough and between said inner andouter surfaces, and exterior finishing material overlying the outersurface of said insulating material. The preferred form of fibrous matfor use in the present invention is a glass fiber mat in which filamentsof glass fiber are bonded together by an adhesive.

Preferably, the fibrous mat-faced gypsum support surface comprises agypsum core having one or more additives therein which improve the waterresistance of the core. As will be seen from examples reported below, astructural member comprising a water-resistant gypsum core faced withglass mat, which itself is hydrophobic, has outstanding weatheringcharacteristics.

An additional preferred form of the present invention comprises a gypsumboard having each of its core faces covered with a porous glass fibermat, with the mat of one of the faces being adhered to the core by setgypsum penetrating but part-way into the thickness of the mat and havingits outer surface substantially free of set gypsum. As will be describedbelow, the glass fiber mat surface, which is free of set gypsum,provides an excellent substrate to which overlying panels of insulationcan be adhered.

In one embodiment of the above form of the invention, the outer surfaceof the mat of the other core face is also substantially free of setgypsum, with set gypsum of the core penetrating but part-way into thethickness of the mat. As will be described below, there aremanufacturing advantages which accompany the production of gypsum boardof such embodiment.

In another embodiment of the aforementioned form of the presentinvention, the set gypsum of the core penetrates substantially throughthe thickness of the mat of the other core face over substantial areaportions thereof in amounts which are sufficient to coat glass fibers ofthe mat with a thin film of set gypsum, but not sufficient to form asmooth, continuous coating of set gypsum. This embodiment in whichsignificant portions of the outer surface of the mat have set gypsumthereon provides a protective surface in a two-board package in whichthe boards are packed together with the gypsum-free surfaces inface-to-face relationship and with the gypsum-covered faces beingexposed. More particularly, this preferred form of board comprises a setgypsum core sandwiched between two adhering sheets of porous glass matof predetermined thickness, each of said mats having an inner and outersurface and comprising randomly distributed glass fibers bonded by anadhesive material, the inner surface of each of said mats being adheredto said gypsum core, and with set gypsum of the core at one surfacethereof penetrating substantially through the thickness of one of saidmats over substantial area portions thereof and coating substantial areaportions of the.outer surface thereof and with set gypsum of the core atthe other surface thereof penetrating but part-way into the thickness ofthe other of said mats, the outer surface of the other of said matsbeing substantially free of set gypsum.

Still another aspect of the present invention comprises a process formaking the aforementioned embodiments of gypsum board, that is, theembodiment in which both outer surfaces of the mats are substantiallyfree of set gypsum and the embodiment in which the outer surface of oneof the mats is substantially free of set gypsum and that of the othermat has set gypsum thereon. The process includes known steps usedheretofore in manufacturing in continuous fashion conventional wallboardand known glass-fiber mat-faced gypsum board, but differs therefrom inthat the viscosity of the aqueous gypsum slurry from which the boardcore is made is controlled in a manner such that the slurry penetratesinto the mats to the extent needed to achieve the desired result. Thebasic steps of the process comprise:

(A) forming an aqueous slurry of calcined gypsum;

(B) continuously feeding said aqueous slurry onto an underlying, movingand supported porous fiber glass mat having a predetermined thicknessand an outer surface;

(C) forming said deposited slurry as it is carried on said moving matinto a panel-like shape; and

(D) applying to the top surface of said panel-like shape of slurry anoverlying porous fiber glass mat of predetermined thickness.

In forming gypsum board in which both of the outer mat surfaces aresubstantially gypsum-free, the viscosity of the slurry is maintained ata value such that portions of said slurry penetrate but part-way throughthe thickness of each of said underlying and overlying mats and thepanel-like shape of slurry is maintained as the calcined gypsum sets toform a set gypsum core having adhered to its surfaces the underlying andoverlying fiber glass mats.

In forming the gypsum-coated/gypsum-free form of glass fiber-facedboard, the viscosity of the slurry is maintained at a value such thatportions of said slurry penetrate substantially through the thickness ofsaid underlying mat over substantial area portions thereof to coatsubstantial area portions of the outer surface and at a value such thatportions of said slurry penetrate but part-way into the thickness ofsaid overlying mat.

There are numerous advantages which flow from the use of the presentinvention. An EISystem which includes a fibrous mat-faced gypsum supportsurface that has affixed thereto insulating material by adhesive only,that is, without fastening means which extend through the insulatingmaterial, has higher tensile or cohesive strength than a like systemwhich includes conventional paper-faced gypsum board. Testing of systemsof this invention which include insulation in the form of expandedpolystyrene panels has shown that initial failure is experienced by apulling apart of the expanded polystyrene panel, thus evidencingimprovement in strength relative to conventional systems where initialfailure is experienced in the paper plies of the gypsum support member.The fibrous mat-faced surface of the gypsum support member is waterresistant in contrast to conventional paper cover sheets of gypsum boardwhich can soak up water. This improved water resistance gives theapplicator greater flexibility in selecting adhesives that can be usedto adhere insulation directly to the mat-faced surface of the gypsumsupport element as adverse affects are not encountered by the use ofwater-based adhesives. The fibrous mat-faced surface of the gypsumsupport element is "nailable", and accordingly, it can be securedreadily to an underlying frame or other substrate by nailing. Incomparison to various of the commercially available systems, theimproved support surface of the present invention has improved rigidityand strength uniformity in both the length and width dimensions of thesystem. Unlike conventional paper cover sheets, the fibrous mat does notexpand or contract during the manufacture of the product; this reducescockle and leads to uniformity of dimensions. The preferred embodimentof the invention which includes the use of a water-resistant coreprovides a substantially improved weather-resistant product which betterresists degradation both within and outside of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a somewhat diagrammatic, fragmentary side elevational viewillustrating portions of a manufacturing line for producing gypsum boardof a type suitable for use in the manufacture of gypsum board preparedfor use in accordance with the present invention;

FIG. 2 is an enlarged fragmentary sectional view, taken as indicatedtoward the left of FIG. 1, of an underlying fiber glass mat used in themanufacture of the gypsum board;

FIG. 3 is a fragmentary plan view taken as indicated by the line 3--3 onFIG. 2;

FIG. 4 is an enlarged sectional view taken as indicated toward the righton FIG. 1 and illustrating both underlying and overlying fiber glassmats, with intervening gypsum composition, used in the manufacture ofthe board;

FIG. 5 is a fragmentary plan view taken as indicated by line 5--5 onFIG. 4;

FIG. 6 is a fragmentary bottom view taken as indicated by the line 6--6on FIG. 4 and illustrating the bottom surface of the underlying mat ofthe board;

FIG. 7 is a transverse sectional view of an edge portion of thecompleted board, this view being taken as indicated by the line 7--7 onFIG. 4;

FIG. 8 is a further enlarged fragmentary sectional view taken asindicated toward the top of FIG. 4;

FIG. 9 is a further enlarged fragmentary sectional view taken asindicated toward the bottom of FIG. 4;

FIG. 10 is a view illustrating two complete gypsum boards fabricatedaccording to the present invention and being assembled for packaging,with the top fibrous mats of the two boards presented toward each other;

FIG. 11 is a view of two boards assembled in the manner indicated inFIG. 10 and bound together for purposes of shipping;

FIG. 12 is a somewhat diagrammatic vertical sectional view through theupper portion of an external building wall, as insulated in accordancewith the present invention; and

FIG. 13 is an enlarged vertical sectional view taken substantially asindicated on FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

The essential components of an EISystem comprise insulating materialwhich is sandwiched between an underlying support surface and anexterior finishing material which can be an integral part of theinsulating material, but which is usually applied to the insulatingmaterial at the site of installation. From one EISystem to the next,there exist variations in structural details and components. Forexample, although the exterior finishing material may be affixeddirectly to the insulating material, various systems include areinforcing component sandwiched between the exterior finishing materialand the insulating material. The reinforcing component comprisesgenerally one or more plies of fiber glass reinforcing fabric or meshwhich is adhered by suitable mastic to the surface of the insulatingmaterial. In some systems, the support surface is affixed to a woodenframe attached to the exterior surface of the outside wall of abuilding, whereas in other systems a metal frame is used. In certainapplications, the support surface may be affixed directly to theexterior surface of an outside wall, for example, one comprising cinderblocks or concrete blocks. In new construction, the support surface istypically affixed directly to the frame of the building. The adhesive ormastic for adhering together components of the system tends to vary fromone system to the next, and typically comprises specially formulatedproprietary compositions. The improved support surface of the presentinvention can be used satisfactorily and to good advantage in EISystemswhich include overlying plies of insulating and exterior finishingmaterials, and other optional components.

Presently, the most popularly used insulating material in EISystems isexpanded or foamed polystyrene, a material which has good moistureresistant properties. Although it has desirably low water vaportransmission, it is not a vapor barrier, but instead is capable ofbreathing. Rigid panels of expanded polystyrene are used most widely inEISystems. Such panels have satisfactory compressive strength andresilience and are presently available in thicknesses ranging from 1/2to 6 inches, widths from 6 to 48 inches and lengths ranging from 4 feetto 16 feet. One commercially available system utilizes rigid, expandedpolystyrene panels which are 2'×4'×1".

Other thermal insulating materials can be used in EISystems also.Examples of such materials include extruded polystyrene, polyurethane,isocyanurate, cement-based insulating plasters, and phenolic foam.Insulating materials generally have low thermal conductivity and lowdensity.

As mentioned above, various EISystems include a reinforcing component,for example, in cloth form, sandwiched between the insulating materialand the exterior finishing material. Glass cloth is most widely used atthe present time to reinforce the system, that is, to improve the impactstrength of the system. The particular type or types of glass cloth usedand the number of plies thereof which are used depend on the impactresistance which is desired. Examples of reinforcing cloth or fabricwhich can be used in the system are woven glass, glass fiber skrim andglass fiber mesh. Installation of the reinforcing fabric generallyinvolves applying a suitable adhesive to the surface of the insulatingmaterial and then applying the fabric thereto. Additional plies offabric can be applied if desired. A cement/acrylic resin is an exampleof an adhesive that can be used.

The exterior finishing material can be affixed directly to theinsulating material or to an intermediate surface such as, for example,the surface of a reinforcing member as described above. The exteriorfinishing material has weathering characteristics and is preferablyappealing in appearance. Presently, the most widely used exterior finishis an acrylic resin-based composition which is available in a paste-typeform which is spread or troweled on the underlying substrate. One typeof such composition can be described as a ready-mixed synthetic resinplaster. After application, the resin sets to form a tough,weather-resistant solid material which adheres tightly to the underlyingsubstrate. Such resin compositions are available commercially in avariety of colors. They include optionally aggregate which can vary insize. This allows the applicator to choose a particular compositionwhich permits him to apply a finish that can vary in texture from fineto coarse. Finishes which have a stucco-like appearance are popular.Small stones of various colors can be embedded in the composition fordecorative purposes.

Examples of other materials that can be used as an exterior finish arePortland cement stucco including, for example, sand and largeraggregate.

The exterior finish can vary in thickness over a wide range, with athickness of about 1/16" to about 1/4" being exemplary.

Turning now to a description of the improved support member for use inexterior systems of the present invention, it comprises a set gypsumcore faced with a fibrous mat. The gypsum core is basically of the typeused in those gypsum structural products which are known as gypsumwallboard, dry wall, gypsum board and gypsum sheathing. The core of sucha product is formed by mixing water with powdered anhydrous calciumsulfate or calcium sulfate hemihydrate (CaSO₄.1/2H₂ O), also known ascalcined gypsum, and thereafter allowing the mixture to hydrate or setinto calcium sulfate dihydrate (CaSO₄.2H₂ O), a relatively hardmaterial. The core of the support member will in general comprise atleast about 85 wt. percent of set gypsum.

The composition from which the set gypsum core is made can includeoptional constituents, including, for example, those includedconventionally in gypsum sheathing. Examples of such constituentsinclude set accelerators, foaming agents, and dispersing agents. As willbe described in more detail below, a preferred gypsum core for use inthe present invention includes one or more additives which improve thewater resistant properties of the core.

The surface of the core to which the insulating material of the systemis affixed is faced with a fibrous mat. The fibrous mat should besufficiently porous to permit water in the aqueous gypsum slurry fromwhich the gypsum core is made to evaporate therethrough. As described indetail below, the gypsum support element for use in the presentinvention can be made efficiently by forming an aqueous gypsum slurrywhich contains excess water and placing thereon the fibrous mat. Aidedby heating, excess water evaporates through the porous mat as thecalcined gypsum sets.

The fibrous mat comprises material which is capable of forming a strongbond with the set gypsum comprising the core of the support surface.Examples of such materials include a mineral-type material such as glassfibers and synthetic resin fibers. The mat can comprise continuous ordiscrete strands or fibers and be woven or nonwoven in form. Nonwovenmats such as chopped strand mat and continuous strand mat can be usedsatisfactorily and are less costly than woven materials. The strands ofsuch mats are bonded together by suitable adhesive. The mat can range inthickness, for example, from about 15 to about 40 mils, with a thicknessof about 25 to about 35 mils being preferred. The aforementioned fibrousmats are known and are commercially available in many forms.

The preferred firous mat is a fiber glass mat comprising fiber glassfilaments oriented in random pattern and bound together with a resinbinder. Fiber glass mats of this type are commercially available, forexample, those sold under the trademark DURA-GLASS by Manville BuildingMaterials Corporation and those sold by ELK Corporation as BUR orshingle mat.

Although improvements in an EISystem can be realized by the use of agypsum core which has but one of its surfaces faced with fibrous mat asdescribed herein, it is preferred that both surfaces of the core befaced with substantially the same fibrous material. If the surfaces ofthe core are faced with materials that have different coefficients ofexpansion, the core tends to warp. Fibrous mat-faced gypsum board andmethods for making the same are known, for example, as described inCanadian Pat. No. 993,779 and U.S. Pat. No. 3,993,822.

As mentioned above, the preferred form of the fibrous mat-faced gypsumsupport surface comprises a gypsum core which has water-resistantproperties. The prcferred means for imparting water-resistant propertiesto the gypsum core is to include in the gypsum composition from whichthe core is made one or more additives which improve the ability of theset gypsum composition to resist being degraded by water, for example,to resist dissolution. In preferred form, the water resistance of thecore is such that it absorbs less than 5 percent water when tested inaccordance with ASTM method C-473 with only the edges exposed.

The fibrous mat for use in the present invention has substantiallybetter water-resistant properties than the conventional paper facing ofgypsum wallboard or sheathing. Nevertheless, evaluations have shown thatthe bond between the fibrous mat and gypsum core can deterioraterelatively quickly under the influence of water. For example, samplesexposed to the weather showed loosening at the glass fiber facing withinone to two months. In contras, evaluations of water-resistant gypsumcore faced with fibrous mat in accordance with the present inventionhave shown the bond between the mat and core resists being degraded bywater for indefinite periods of time.

Examples of materials which have been reported as being effective forimproving the water-resistant properties of gypsum products are thefollowing: poly(vinyl alcohol), with or without a minor amount ofpoly(vinyl acetate); metallic resinates; wax or asphalt or mixturesthereof; a mixture of wax and/or asphalt and also cornflower andpotassium permanganate; water insoluble thermoplastic organic materialssuch as petroleum and natural asphalt, coal tar, and thermoplasticsynthetic resins such as poly(vinyl acetate), poly(vinyl chloride) and acopolymer of vinyl acetate and vinyl chloride and acrylic resins; amixture of metal rosin soap, a water soluble alkaline earth metal salt,and residual fuel oil; a mixture of petroleum wax in the form of anemulsion and either residual fuel oil, pine tar or coal tar; a mixturecomprising residual fuel oil and rosin; aromatic isocyanates anddiisocyanates; organohydrogenpolysiloxanes; a wax-asphalt emulsion withor without such materials as potassium sulfate, alkali and alkalineearth aluminates, and Portland cement; a wax-asphalt emulsion preparedby adding to a blend of molten wax and asphalt an oil-soluble,water-dispersible emulsifying agent, and admixing the aforementionedwith a solution of casein which contains, as a dispersing agent, analkali sulfonate of a polyarylmethylene condensation product.

A preferred material for use in improving the water-resistant propertiesof the gypsum core comprises wax-asphalt emulsion, species of which areavailable commercially. The wax portion of the emulsion is preferably aparaffin or microcrystalline wax, but other waxes can be used also. Theasphalt in general should have a softening point of about 115° F., asdetermined by the ring and ball method. The total amount of wax andasphalt in the aqueous emulsion will generally comprise about 50 to 60wt. % of the aqueous emulsion, with the weight ratio of asphalt to waxvarying from about 1 to 1 to about 10 to 1. Various methods are knownfor preparing the wax-asphalt emulsion, as reported in U.S. Pat. No.3,935,021 to D. R. Greve and E. D. O'Neill assigned to the same assigneeas the present invention. Commercially available wax asphalt emulsionsthat can be used in the composition of the present invention are sold byUnited States Gypsum Co. (Wax Emulsion), Monsey Products, (No. 52Emulsion) and Douglas Oil Co. (Docal No. 1034). The amount ofwax-asphalt emulsion used can be within the range of about 3 to about 10wt. %, preferrably about 5 to about 7 wt. %, based on the total weightof the ingredients of the composition from which the set gypsum core ismade, said ingredients including the water of the wax-asphalt emulsion,but not including additional amounts of water that are added to thegypsum composition for forming an aqueous slurry thereof.

A particularly preferred material for use in improving thewater-resistant properties of the gypsum core comprises a mixture ofmaterials, namely, poly(vinyl alcohol) and wax-asphalt emulsion of theaforementioned type. The use of such additives to improve the waterresistance of gypsum products is described in aforementioned U.S. Pat.No. 3,935,021.

The source of the poly(vinyl alcohol) is preferably a substantiallycompletely hydrolyzed form of poly(vinyl acetate), that is, about 97 to100% hydrolyzed polyvinyl acetate. The poly(vinyl alcohol) should becold-water insoluble and soluble in water at elevated temperatures, forexample, at temperatures of about 140° to about 205° F. In general, a 4wt. % water solution of poly(vinyl alcohol) at 20° C. will have aviscosity of about 25 to 70 cp as determined by means of the Hoepplerfalling ball method. Commercially available poly(vinyl alcohols) for usein the composition of the present invention are available from E. I. duPont de Nemours and Company, sold under the trademark "Elvanol" and fromMonsanto Co., sold under the trademark "Gelvatol". Examples of suchproducts are Elvanol, Grades 71-30, 72-60, and 70-05, and Gelvatol,Grades 1-90, 3-91, 1-60, and 3-60. Air Products Corp. also sells theproduct as WS-42.

The amounts of poly(vinyl alcohol) and wax-asphalt emulsion used shouldbe at least about 0.05 wt. % and about 2 wt. % respectively. Thepreferred amounts of poly(vinyl alcohol) and wax-asphalt emulsion areabout 0.15 to about 0.4 wt. % and about 3.0 to about 5.0 wt. %respectively. Unless stated otherwise, the term "wt. %" when used hereinand in the claims means weight percent based on the total weight of theingredients of the composition from which the set gypsum core is made,said ingredients including the water of the wax-asphalt emulsion, butnot including additional amounts of water that are added to the gypsumcomposition for forming an aqueous slurry thereof.

An attractive feature of the present invention is that the fibrousmat-faced gypsum support member can be made utilizing existing wallboardmanufacturing lines, for example, as shown somewhat diagramatically inFIG. 1. In conventional fashion, dry ingredients (not shown) from whichthe gypsum core is formed are pre-mixed and then fed to a mixer of thetype commonly referred to as a pin mixer 2. Water and other liquidconstituents (not shown) used in making the core are metered into thepin mixer 2 where they are combined with the dry ingredients to form anaqueous gypsum slurry. Foam is generally added to the slurry in the pinmixer to control the density of the resulting core. The slurry 4 isdispersed through one or more outlets at the bottom of the mixer 2 ontoa moving sheet of fibrous mat 6. The sheet of fibrous mat 6 isindefinite in length and is fed from a roll (not shown) of the mat.

As is common practice in the manufacture of conventional paper-facedgypsum board, the two opposite edge portions of the fibrous mat 6 areprogressively flexed upwardly from the mean plane of the mat 6 and thenturned inwardly at the margins as to provide coverings for the edges ofthe resulting board 40. In FIG. 1, this progressive flexing and shapingof the edges of the mat 6 are shown for only one side edge of the matand the conventional guiding devices which are ordinarily employed forthis purpose are omitted from the figure for the sake of clarity. FIG. 7shows an edge of the set gypsum core 42 covered by the overlapped edgeportion 6A of the mat 6. FIG. 7 shows also score marks 10 and 10A of themat 6, the score marks permitting the formation of good edges and flatsurfaces. The score marks 10 and 10A are made by a conventional scoringwheel 12. An advantage of using the preferred form of glass fiber mat isthat it is capable of being scored and edged like conventional paperfacing.

Another sheet of fibrous mat 16 is fed from a roll (not shown) onto thetop of the slurry 4, thereby sandwiching the slurry between the twomoving fibrous mats which form the facings of the set gypsum core 42which is formed from the slurry. The mats 6 and 16 with the slurry 4sandwiched therebetween enter the nip between the upper and lowerforming or shaping rolls 18 and 20, and are thereafter received on aconveyer belt 22. Conventional edge guiding devices, such as indicatedat 24 shape and maintain the edges of the composite until the gypsum hasset sufficiently to retain its shape. In due course, sequential lengthsof the board are cut and further processed by exposure to heat whichaccelerates the drying of the board by increasing the rate ofevaporation of excess water in the gypsum slurry.

With reference to FIG. 7, it has been observed that the set gypsum ofthe core 42 is effective in forming satisfactory bonds with the mats andbetween the edge portions of the overlying mat 16 and the overlappededge portion 6A of the underlying mat 6, thus making it unnecessary touse a bond improver in the slurry or an edge paste to form theaforementioned bonds.

The preferred form of mats 6 and 16, as shown in FIGS. 2 and 3,comprises glass fiber filaments 30 oriented in random pattern and boundtogether with a resin binder (not shown).

A preferred form of glass fiber mat-faced gypsum board 40 is shown inFIGS. 4 and 7. It comprises one in which the set gypsum of the core 42penetrates substantially through the thickness of the mat 6 oversubstantial area portions thereof and in which the set gypsum of thecore 42 penetrates the mat 16 partially, with the surface being thussubstantially free of set gypsum. The gypsum-free surface of mat 16, asseen in FIG. 8, is highly textured, and provides an excellent substratefor adhering thereto an overlying component inasmuch as it comprisesmany interstices into which an adhesive composition can flow and bond.

In shipping gypsum board, it is convenient to package two boards 40 and40A together (see FIGS. 10 and 11), with the glass fiber gypsum-freesurfaces 41 and 41A in face to face relationship, and thus protected,and with the gypsum-coated surfaces (for example, 43A in FIG. 11)forming the outside of the package. The set gypsum on the outsidesurfaces helps to keep the board from being damaged during handling,shipping and storage, and protects the skin of those who come in contactwith the board from being irritated by the glass fibers of the mat.

The phrase "substantially penetrated by set gypsum", as used herein,means that the set gypsum of the core, extends from the mat surfacewhich is contiguous to the core to the outer mat surface and coats glassfibers on the outer surface with a thin film of set gypsum to the extentthat the outline of glass fibers can be seen through the thin film ofset gypsum. The phrase "over substantial area portions of the outersurface", as used herein, means that about 30 to about 75% of the outersurface area of the mat is substantially penetrated by set gypsum.Preferably, about 45 to about 55% of the outer surface area of the matis substantially penetrated by set gypsum. Accordingly, thegypsum-coated surface of this preferred embodiment of the boardcomprises a surface that has a roughened or patterned appearance; itdoes not comprise a smooth continuous coating of set gypsum. Thispreferred form of board can be formed with relatively small amounts ofgypsum slurry being deposited on the underlying support surface, thusminimizing the need to clean the surface.

The need for such cleaning can be substantially avoided by adjusting theviscosity of the slurry so that it penetrates but part-way through theunderlying fibrous mat, for example, up to about 50% of its thickness.Thus, this preferred form of board has two gypsum-free fiber-facedsurfaces.

The manufacture of the aforementioned preferred forms of board can beaccomplished by controlling the viscosity of the aqueous slurry of thecalcined gypsum in a manner such that the slurry penetrates theunderlying and overlying mats to the desired degree. In manufacturingeach of the aforementioned preferred forms of board, the viscosity ofthe slurry should be such that it penetrates about 10 to 50% of thethickness of the overlying mat over the entire surface area thereof.

The recommended means for controlling the viscosity of the slurry is toadd thereto a viscosity-control agent. Such viscosity-control agents areknown in the field of gypsum board manufacture. A preferredviscosity-control agent is paper fiber. Examples of other agents thatcan be used are cellulosic thickeners, bentonite clays and starches.

The particular viscosity values that are used in the manufacturingoperation can vary from one application to the next, depending on theporosity of the mat, and the desired penetration of the slurry.Accordingly, for any particular application, the viscosity value is bestdetermined empirically.

In using the preferred form of glass fiber mat, as described above, tomanufacture the aforementioned preferred forms of board, developmentalwork has shown that satisfactory results can be achieved utilizing agypsum slurry having a viscosity within the range of about 5000 to 7000cp. As used herein, the viscosity value refers to Brookfield viscositymeasured at a temperature of 70° F. at 10 rpm utilizing paddle No. 3. Itshould be appreciated that the amount of viscosity-control agent addedto the slurry to give the desired viscosity will vary depending on theparticular agent used and the specific viscosity desired.

In preferred form, the core of the fibrous mat-faced gypsum board has adensity of about 40 to about 50 lbs/cubic ft., most preferably about 42to about 45 lbs/cubic ft. The manufacture of cores having densitieswithin the preferred range can be effected by using known techniques,for example, by introducing an appropriate amount of foam into theaqueous gypsum slurry from which the core is formed. There are weightadvantages that can be realized by the use of fibrous mat-faced gypsumboard in EISystems in that fibrous mats which are lighter in weight thanconventional paper facing are available. For example, the weight of awidely used paper facing in the manufacture of conventional gypsumsheathing is in the range of about 120 lbs/1000 sq. ft. of board,whereas the weight of a preferred form of glass fiber mat for use in thepresent invention is about 40 lbs/1000 sq. ft of board.

Turning now to FIGS. 12 and 13, there is shown therein an example of anexterior insulating system fabricated in accordance with the presentinvention and comprising the exterior portion of the building 81. TheEISystem 80 comprises panels of fibrous mat-faced board 82 affixed bynails 84 to wood framing 86. A foamed polystyrene panel 88, about 1 inchthick, is adhered to the fibrous mat-faced board 82 by adhesive 90. Areinforcing member comprising glass fiber skrim 92 is sandwiched betweenthe polystyrene panel 88 and the final finishing material 94 by adhesive96.

Various of the preferred forms of the gypsum board of the presentinvention can be used also to good advantage in place of conventionalgypsum sheathing in applications other than EISystems. Thus, thepreferred forms of board can be used as an underlying support surfacewhich is covered with overlying finishing materials, for example,aluminum, wood siding, plaster and Portland cement stucco.

EXAMPLES

The formulation set forth below is an example of a preferred aqueousgypsum slurry which can be used in making the core of a gypsum supportmember in accordance with the present invention.

    ______________________________________    Constituents      Lbs./1000 sq. ft. of board    ______________________________________    calcined gypsum   1380    (CaSO.1/2 H.sub.2 O)    wax/asphalt emulsion                      130    aqueous solution of 10 wt %                      56    poly(vinyl alcohol)    paper fiber       15    set accelerator    6    ammonium lauryl sulfonate                       1    (foaming agent)    calcium lignosulfonate                       2    (dispersing agent)    water             260    ______________________________________

The wax/asphalt emulsion used in the above formulation containedapproximately 48 wt. % solids of which about 11 wt. % was paraffin waxand about 37 wt. % was asphalt. The set accelerator comprised about 80wt. % potash, about 12 wt. % lignosulfonate and about 8 wt. % groundgypsum.

The above formulation was used to prepare gypsum board, the surfaces ofwhich were covered with nonwoven fiber glass mat. The mat was composedof glass fiber filaments oriented in a random pattern bonded together byan adhesive referred to by the manufacturer as a "modifiedurea-formaldehyde resin". The mat had a thickness of 33 mils, was moreporous than paper of the type used as the cover sheet of gypsumwallboard, and was not significantly weakened by water. The airpermeability of the mat was 700 CFM/sq. ft. (test method FG 436-910).The mat is available commercially as DURA-GLASS 7502-2 lbs. and is anexample of a preferred fibrous mat for use in the practice of thepresent invention.

Continuous length board was made from the above gypsum slurry and glassfiber mat on a conventional wallboard machine. The slurry was fed onto amoving sheet of the mat as it was unrolled from a roll onto a movingsupport surface. The mat had a width of about 51 inches and was scoredcontinuously by conventional scoring blades prior to the deposition ofthe slurry thereon. Each edge of the mat was scored with two scoremarks, with each of the outer scores being about 1 inch from itsrespective edge of the mat and each of the inner scores being about 11/2inch from its respective edge. After the slurry was deposited on themat, the edges were folded at the score marks and overlapped on top ofthe slurry. (The gypsum core formed from this operation had a width of477/8 inches and a thickness of 1/2 inch.) Mat from another roll thereofand having a width of 471/2 inches was fed onto the top of the gypsumslurry and the overlapped edge portions of the underlying mat. Thegypsum slurry penetrated the overlapped edge portions and served to bondthe edge portions of the overlying mat to the overlapped edge portionsof the underlying mat.

The viscosity of the gypsum slurry was about 5900 cp at 70° F. At thisviscosity, the slurry penetrated substantially through some portions ofthe underlying mat to form a thin film thereof on about 40 to 50% of thearea of the outer surface of the mat. As the gypsum in the film set,substantial portions of the outer surface of the mat were covered with athin film of set gypsum. The surface had a roughened appearance withoutlines of the glass filaments being observable underneath the thincoatings of gypsum which covered them. However, at the aforementionedviscosity, the slurry penetrated but a portion (about 5 mils) of thethickness of the overlying mat over the entire area thereof, with noslurry being observed on the outer surface of the mat. As the gypsum setin the intermediate portions of the mat that were penetrated by theslurry, it formed a bond that included a mechanical interlock with theset gypsum core.

The continuous length board is cut into lengths of about 8 feet. Dryingof the gypsum board is accelerated by heating in an oven at 350° F. forabout 2 hours and until the board is almost dry and then at 200° F. forabout 1 hour until it is dried completely. The density of the board isabout 43 lb. cu.ft.

The gypsum-free surfaces of panels (2'×2') of glass fiber-faced boardsas described above were adhered to panels of expanded polystyreneutilizing two different commercially available adhesive systems. In onesystem, hereafter "System A", one of the faces of a panel of expandedpolystyrene having a thickness of about 1 inch and 2'×2' was smearedwith an adhesive mixture comprising cement, sand, and resin binderutilizing a 3/8"×3/8" toothed trowel. The panel was then adhered to theglass fiber-faced gypsum board. Thereafter, glass fiber reinforcing meshwas applied to the other face of the panel of expanded polystyrene and adecorative finish was applied to the mesh.

In the other system, hereafter "System B", the same steps as describedabove for System A were followed except that an acrylic adhesive wasapplied to the gypsum-free surface of the board and the polystyrenepanel adhered thereto.

Two additional systems like Systems A and B above were assembled, exceptthat conventional paper-faced gypsum sheathing was substituted for theglass fiber-faced gypsum board in each of Systems A and B.

The integrity of each of the systems was evaluated using 11/2"×11/2"cross-sectional cubes which were extracted from the systems and whichwere pulled apart in a tensile test apparatus. The results of thetesting are set forth below.

    ______________________________________               Fiber Glass-  Paper-    System     Faced Board   Faced Board    ______________________________________    A          100% break in 66% break in the               the polystyrene                             paper, 33% break               panel         in the polystyrene    B          100% break in 100% break in the               the polystyrene                             paper               panel    ______________________________________     From the above results, it can be seen that the use of the glass     fiber-faced gypsum support surface improved significantly the strength of     the assembly in that tensile failure was transferred from the paper cover     of the gypsum sheathing to the foamed polystyrene, with no failure at all     experienced in the glass fiber mat or the gypsum core to which it was     adhered. Thus, it should be appreciated that, in accordance with the     present invention, the integrity of an EISystem can be improved     significantly because it is no longer dependent upon the ply strength of a     paper cover sheet, but upon a component having much higher strength.

Glass fiber-faced gypsum boards, made as described above, and with theiredges protected, were placed outdoors for several months and exposed tothe elements. During that period, the boards were exposed to about 20inches of rain. After this exposure, the boards were examined and foundto be in excellent condition with no signs of deterioration.

Other outdoor tests have shown that glass fiber mat-faced gypsum boardin accordance with the present invention and having a core whichincludes wax-asphalt emulsion as a water-resistant additive betterresists deterioration than a like board having a core which includessodium methyl siliconate as the water-resistant additive.

Gypsum board comprising a set gypsum core faced with a fibrous mat, asdescribed herein, and preferably gypsum board comprising a set gypsumcore sandwiched between two sheets of porous glass mat, can be used toparticular advantage also as a component of a shaft wall assembly orsimilar assembly in the interior of a building. In such application, thefibrous mat-faced board can be used to particular advantage in place ofconventional paper-faced gypsum core board or shaft liner panels, thecore of which generally includes fire-resistant additives. Assemblies ofthis type generally comprise metal framework or studs for support of thegypsum panels which form the walls of the shafts of elevators,stairwells and the like. Examples of such assemblies are shown in U.S.Pat. Nos. 4,047,355; 4,324,082 and 4,364,212, the disclosures of whichare incorporated herein by reference. Fibrous mat-faced board, asdescribed herein, can be used, for example, in the assemblies describedin the aforementioned patents, and particularly as the shaft linerpanel. For use in such application, the core of the board can includefire resistant additives.

In summary, it can be said that the present invention provides in apractical way important functional improvements in exterior finishingsystems for buildings, including particularly exterior insulatingsystems , and in shaft wall assemblies.

We claim:
 1. Gypsum board comprising a set gypsum core sandwichedbetween two sheets of porous glass mat, each of which has an inner andouter surface, said mat comprising randomly distributed glass fibersbonded by an adhesive material, the inner surface of each of said matsadhered to said gypsum core by a portion of the set gypsum comprisingsaid core, the outer surface of one of said mats having portions thereofcoated with set gypsum comprising portions of the set gypsum of saidcore, and the outer surface of the other of said mats beingsubstantially free of set gypsum.
 2. Gypsum board according to claim 1wherein said mat is a glass fiber mat comprising randomly distributedglass filaments bonded by an adhesive material.
 3. Gypsum board inaccordance with claim 1 wherein each of said mats comprises randomlydistributed glass filaments bonded by an adhesive material, wherein saidgypsum-coated mat is substantially penetrated by set gypsum oversubstantial area portions of the outer surface thereof, and wherein theset gypsum of the core penetrates but part-way into the thickness of theother of said mats.
 4. Gypsum board in accordance with claim 3 whereinabout 45 to about 55% of the outer surface of said gypsum-coated mat issubstantially penetrated by the set gypsum.
 5. Gypsum board inaccordance with claim 1 or 3 in the form of a package in which two ofsaid boards are packaged with said gypsum-free outer surfaces in face toface relationship and in which said gypsum-coated outer surfaces formthe outer surfaces of said package.
 6. Gypsum board comprising a setgysum core sandwiched between two sheets of porous glass mat, each ofwhich has an inner and outer surface and a predetermined thickness, saidmat comprising randomly distributed glass fibers bonded by an adhesivematerial, the inner surface of each of said mats adhered to said gypsumcore by set gypsum of said core penetrating but part-way into thethickness of each of said mats, and wherein the outer surface of each ofsaid mats is substantially free of set gypsum.
 7. Gypsum boardcomprising a set gypsum core sandwiched between two sheets of porousglass mat, each of which has an inner and outer surface, said matoomprising randomly distributed glass fibers bonded by an adhesivematerial, the inner surface of each of said mats adhered to said gypsumcore by set gypsum of said core penetrating but part-way into thethickness of each of said mats, with the interstices between the fibersat the inner surface of each of said mats being substantially filledwith set gypsum, and wherein the outer surface of each of said mats issubstantially free of set gypsum.
 8. Gypsum board comprising the setproduct of an aqueous slurry of calcined gypsum of predeterminedviscosity sandwiched between underlying and overlying sheets of porousglass mat, each of which has an inner and outer surface and apredetermined thickness, said mat comprising randomly distributed glassfibers bonded by an adhesive material, wherein the relationship of theviscosity of said slurry to the porosity and thickness of each of saidmats is such that said slurry penetrates but part-way into the thicknessof each of said mats as said slurry sets to form a set gypsum corehaving adhered thereto said mats, the outer surfaces of which aresubstantially free of set gypsum.
 9. Gypsum board according to claim 8wherein the thickness of each of said mats is about 15 to about 40 milsand wherein the viscosity of said slurry is about 5000 to about 7000 cpat 70° F.
 10. Gypsum board according to claim 9 wherein said slurrypenetrates about 10 to 50% of the thickness of the overlying mat. 11.Gypsum board according to claim 9 wherein said slurry penetrates up toabout 50% of the thickness of said underlying mat.
 12. Gypsum boardaccording to claim 8, 9, 10, or 11 wherein said set product includespaper fiber.
 13. Gypsum board according to claim 12 wherein the airpermeability of each of said mats is about 700 CFM/sq. ft.
 14. Gypsumboard according to claim 12 wherein the thickness of each of said matsis about 25 to about 35 mils.
 15. Gypsum board comprising a set gypsumcore sandwiched between two sheets of porous glass fiber mat, each ofthe mats having an inner and outer surface, the inner surface of each ofsaid mats adhered to said gypsum core by set gypsum of said corepenetrating but part-way into the thickness of each of said mats, withthe interstices between the fibers at the inner surface of each of saidmat being substantially filled with set gypsum, and the outer surface ofeach of said mats being substantially free of set gypsum and comprisingmany interstices into which an adhesive composition can flow and bond.16. Gypsum board according to claim 15 wherein each of said matscomprises randomly distributed glass fibers bonded by an adhesivematerial.
 17. A process for manufacturing in continuous fashion a glassfiber mat-faced gypsum board of indefinite length comprising:(A) formingan aqueous slurry of calcined gypsum; (B) continuously feeding saidaqueous slurry onto an underlying, moving and supported porous glassfiber mat having an outer surface; (C) forming said deposited slurry asit is carried on said moving mat into a panel-like shape; (D) applyingto the top surface of said panel-like shape of slurry an overlyingporous glass fiber mat of predetermined thickness; (E) maintaining theviscosity of said slurry at a value such that said underlying mat issubstantially penetrated by said slurry over substantial area portionsof the outer surface thereof, and at a value such that portions of saidslurry penetrate but part-way into the thickness of said overlying mat;and (F) maintaining said panel-like shape as said calcined gypsum setsto form a set gypsum core having adhered to one surface thereof saidunderlying glass fiber mat which is substantially penetrated by setgypsum over substantial area portions of the outer surface thereof, andthe core having adhered to its other surface said overlying glass fibermat, the outer surface of which is substantially free of set gypsum. 18.A process according to claim 17 wherein said mat comprises randomlydistributed glass filaments bonded by an adhesive material and whereinthe viscosity of said slurry is about 5000 to about 7000 cp at 70° F.19. A process for manufacturing in continuous fashion a glass fibermat-faced gypsum board of indefinite length comprising:(A) forming anaqueous slurry of calcined gypsum; (B) continuously feeding said aqueousslurry onto an underlying, moving and supported porous glass fiber mathaving an outer surface and a predetermined thickness; (C) forming saiddeposited slurry as it is carried on said moving mat into a panel-likeshape; (D) applying to the top surface of said panel-like shape ofslurry an overlying porous glass fiber mat having an outer surface and apredetermined thickness; (E) maintaining the viscosity of said slurry ata value such that portions of said slurry penetrate but part-way intothe thickness of each of said underlying and overlying mats; and (F)maintaining said panel-like shape as said calcined gypsum sets to form aset gypsum core having adhered thereto said mats, the outer surfaces ofwhich are substantially free of set gypsum.
 20. A process formanufacturing in continuous fashion a glass fiber mat-faced board ofindefinite length comprising:(A) forming an aqueous slurry of calcinedgypsum; (B) continuously feeding said aqueous slurry onto an underlying,moving and supported porous glass fiber mat having an inner and outersurface and a predetermined thickness; (C) forming said deposited slurryas it is carried on said moving mat into a panel-like shape; (D)applying to the top surface of said panel-like shape of slurry anoverlying porous glass fiber mat having an inner and outer surface and apredetermined thickness; (E) maintaining the viscosity of said slurry ata value such that the relationship between the viscosity of said slurryto the porosity and thickness of each of said underlying and overlyingmats is such that said slurry penetrates but part-way into the thicknessof each of said mats; and (F) maintaining said panel-like shape as saidcalcined gypsum sets to form a set gypsum core to which said underlyingand overlying mats are adhered by said set gypsum which substantiallyfills the interstices between the individual glass fibers at the innersurfaces of said mats, with the interstices between the individualfibers at the outer surfaces of said mats being substantially free ofset gypsum.
 21. A process for manufacturing in continuous fashion aglass mat-faced gypsum board of indefinite length comprising:(A) formingan aqueous slurry of calcined gypsum; (B) continuously feeding saidaqueous slurry onto an underlying, moving and supported porous glass mathaving an outer surface and a predetermined thickness; (C) forming saiddeposited slurry as it is carried on said moving mat into a panel-likeshape; (D) applying to the top surface of said panel-like shape ofslurry on overlying porous glass mat having an outer surface and apredetermined thickness; (E) including in said slurry paper fibers in anamount such that portions of said slurry penetrate but part-way into thethickness of each of said underlying and overlying mats; and (F)maintaining said panel-like shape as said calcined gypsum sets to form aset gypsum core having adhered thereto said mats, the outer surfaces ofwhich are substantially free of set gypsum.
 22. A process according toclaim 19 or 20, including adding to said slurry paper fibers.
 23. Aprocess according to claim 19, 20 or 21 wherein said mats are glassfiber mats comprising randomly distributed glass filaments bonded by anadhesive material.
 24. A process according to claim 23 wherein thethickness of each of said mats is about 15 to about 40 mils.
 25. Aprocess according to claim 24, wherein the thickness of each of saidmats is about 25 to about 35 mils.
 26. A process according to claim 24,wherein the viscosity of said slurry is about 5000 to about 7000 cp at70° F.
 27. A process according to claim 26, wherein the air permeabilityof each of said mats is about 700 CFM/sq. ft.
 28. A process according toclaim 19, 20 or 21 wherein said slurry penetrates up to about 50% of thethickness of said underlying mat.
 29. A process according to claim 28wherein said mats are glass fiber mats comprising randomly distributedglass filaments bonded by an adhesive material.
 30. A process accordingto claim 19, 20 or 21 wherein said slurry penetrates about 10 to 50% ofthe thickness of the overlying mat.
 31. A process according to claim 30wherein said mats are glass fiber mats comprising randomly distributedglass filaments bonded by an adhesive material.
 32. A process accordingto claim 31 wherein said slurry penetrates up to about 50% of thethickness of said underlying mat.